Bake angel food cake as directed on box. Let cool upside down.
To make frosting, in electric mixer, mix whipping cream until soft peaks form.Slowly add confectioners' sugar and cocoa powder. Once medium peaks form, remove from stand mixer and fold in Heath Bar crumbles.
Note: I suggest taste testing the frosting after sugar and cocoa are added. Sweetness can be altered based on your preferences, but note that Heath bar crumbles will add some additional sweetness to frosting.